1. Field of Invention
Various embodiments of the present invention relate to an integrated circuit, and more particularly, to an image sensor.
2. Related Art
In general, an image sensor refers to a device which captures an image by using semiconductor properties that respond to light. charge coupled device (CCD) image sensors have been widely used. However, as complementary metal oxide semiconductor (CMOS) technology has made rapid progress, an image sensor using CMOS has been developed. As compared to a conventional CCD image sensor, CMOS image sensors have an advantage in that analog circuits, which include pixel arrays, and digital control circuits can be directly implemented on a single integrated circuit (IC).
An image sensor has as many comparators as the number of columns of a pixel array. Since the comparator is a circuit requisite to convert a pixel signal into a digital signal, it affects the quality of an output image. The comparator receives a ramp signal and a data signal, i.e., a pixel signal related to an image provided from an individual pixel. The ramp signal gradually decreases at a constant rate. The comparator compares the data signal with the ramp signal to output values that are stored as an image. Therefore, it is important to generate a reliable ramp signal from an internal ramp signal generation circuit so that an image sensor can store a reliable image.